Write the chemical symbols for three different atoms or atomic cations with 18 electrons.

Chlorine has 17 electrons in it natural state but it gains an electron and becomes an anion with 18 electrons. 

Potassium (K) has 19 electrons in its natural state. It loses an electron and becomes K+ and then is left with 18 electrons .

The atomic number of calcium is 20 i.e. Ca has 20 electrons.It Loses 2 electrons and becomes Ca++ and  has 18 electrons.

Firstly, the water in the dams hold gravitational potential energy as they are above ground level. the gravitational potential energy is then transferred to kinetic energy as it falls, spinning the turbinethe turbine then spins the generator, which is a large magnet surrounded by metal coils. by doing this, the generator generates electricity. in this action, the energy transfer taken place is kinetic to electric energy